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Define all Pdb's instance variable in __init__ #140790
Description
Pdb currently have a few instances variables that are not defined in __init__.
Mainly as far as I can tell, :
self.lineno self.stack self.curindex self.curframe self.currentbp self._user_requested_quit
(not set in Bdb, or Cmd superclass either)
This means that accessing these requires a hasattr/getattr, which we can see in the Pdb's implementation in a few places. This is a footgun for a subclasses, and in particular for IPython, in some circumstances, the gettattr start to have a non-negligible perf impact (We support things like having __debuggerskip__ = True|False in a frame, so the getattr(self, 'currentframe',...) start to get expensive.
It would be great if all those were initialized in __init__; Yes I can initialize in my __init__ subclass, but having it in CPython should benefit everybody, plus it would allow the removal of a few getattr() in CPython source directly.
Personally I care mostly about curframe, but while at it maybe do the other ones.
I am not aware of anything that uses the fact the attribute is missing.
Activity
pdb: Initialize instance variables in Pdb.__init__
pythongh-140790: pdb: Initialize instance variables in Pdb.__init__
pythongh-140790: pdb: Initialize instance variables in Pdb.__init__
picnixz commented on Oct 30, 2025
I think curframe can be changed but currentbp seems to be an attribute of Bdb instead of Pdb.
cc @gaogaotiantian
gaogaotiantian commented on Oct 30, 2025
I need some time to take a deeper look into this. It might be a breaking change for other debuggers besides IPython. In general I agree that it would be much better if we can just define everyting in __init__. In practice, pdb has been there for many years and any issue could be a feature people rely on.
I still think we can probably move forward on this, just need some careful review and thought.
pythongh-140790: pdb: Initialize instance variables in Pdb.__init__
lysnikolaou commented on Nov 12, 2025
I did a semi-thorough look around GitHub to see whether there's any code that depends on curframe not existing. I couldn't find anything. Also, the attached PR does not change currentbp.
@gaogaotiantian Does this maybe help push the attached PR forward? Is there anything else that we can do that would make the decision to merge easier?
gaogaotiantian commented on Nov 14, 2025
@lysnikolaou yes that is very helpful. The other attributes are safer. self.curframe was there for too long and I'm a bit hesitated, glad to know that there's no code that we can find to rely on it.
gh-140790: pdb: Initialize instance variables in Pdb.__init__ (#140791)
Carreau commented on Nov 17, 2025
Thanks for the quick review and the merge!
pythongh-140790: pdb: Initialize instance variables in Pdb.__init__ (p…